Somatic cell nuclear transfer

Cloning by nuclear transfer from adult somatic cells is a remarkable demonstration of developmental plasticity. When a nucleus is placed in oocyte cytoplasm, the changes in chromatin structure that govern differentiation can be reversed, and the nucleus can be made to control development to term.     

Developmental plasticity in the visual and auditory representations in the mammalian superior colliculus

Environmental factors play an important role in certain aspects of the development of sensory systems. But the way in which the maturation of different sensory modalities is coordinated is poorly understood. We have investigated this question neurophysiologically in the mammalian superior colliculus (SC), which contains topographically aligned maps of visual and auditory space. We report here that an essentially normal auditory map, in approximate register with the visual map, is found in the SC of adult ferrets reared with abnormal binaural localization cues. Also, if, early in life, one eye is deviated laterally, there is a compensatory shift in the auditory map, but early eye rotation totally disorders the auditory representation. These results imply that development of the auditory map is affected by visual activity or by information about eye position and that there is definite, but limited, capacity for the auditory map to reorganize so that it remains aligned with the visual map.     

A new fixative for smoked kymographic tracings

Résumé Une dilution de polybutyl méthacrylate dans de l'acétone anhydre (rapport 1 à 7) est proposée comme fixateur d'enregistrements sur papier enfumé. Ce nouveau fixateur est incolore, sèche vite, rend les enregistrements flexibles et est peu coûteux.     

Protein-only transmission of three yeast prion strains

Key questions regarding the molecular nature of prions are how different prion strains can be propagated by the same protein and whether they are only protein. Here we demonstrate the protein-only nature of prion strains in a yeast model, the [PSI] genetic element that enhances the read-through of nonsense mutations in the yeast Saccharomyces cerevisiae. Infectious fibrous aggregates containing a Sup35 prion-determining amino-terminal fragment labelled with green fluorescent protein were purified from yeast harbouring distinctive prion strains. Using the infectious aggregates as 'seeds', elongated fibres were generated in vitro from the bacterially expressed labelled prion protein. De novo generation of strain-specific [PSI] infectivity was demonstrated by introducing sheared fibres into uninfected yeast hosts. The cross-sectional morphology of the elongated fibres generated in vitro was indistinguishable from that of the short yeast seeds, as visualized by electron microscopy. Electron diffraction of the long fibres showed the 4.7 A spacing characteristic of the cross-beta structure of amyloids. The fact that the amyloid fibres nucleated in vitro propagate the strain-specific infectivity of the yeast seeds implies that the heritable information of distinct prion strains must be encoded by different, self-propagating cross-beta folding patterns of the same prion protein.